The current concepts of cell ragulation has led to a hypothesis that is difficult to biochemically and biologically analyze. I have developed a culture system which allows experimental study of growth cycle regulation, and I have shown the serious limitations of the previously used cell systems for the study of growth control. Serum control of cellular growth has been shown to be regulated in two discrete phases: competence and progression. I have proposed the study of the processes involved in competence and progression. The understanding of these processes will provide valuable knowledge concerning cell regulation. Competence is induced by a platelet derived mitogen. The biochemical processes by which competence is induced are not known. The experiments proposed in this grant are designed to elucidate the processes by which competence is formed. Since SV40 abrogate the cellular growth requirement for the platelet mitogen, it is important to determine if transformation induces the normal biochemical process which renders the cell competent. This proposed work will allow the study, cellular and biochemical, of the process of commitment (that point at which the cell is committed to DNA synthesis). The analysis of this process will greatly enhance our knowledge of cell cycle control. I have proposed work to show how viral transformation alters normal cell regulation. These findings can lead to a model that describes the mechanism by which normal cell regulation is lost.